Rotatively-set anchor assembly for a mine bolt



Oct. 3L E967 cz. 1. WILLIAMS 3,349,552

RTATIVELYSET ANCHOR ASSEMBLY FOR A MINE BQLT Filed June 23, 1965 5 Sheets-Sheet l Oct. 31, w67 c. l. WILLIAMS 3,349,652

ROTTIVELYSET ANCHOR ASSEMBLY FOR A MINE BOLT Filed June 25, 1965 5 Sheets-Sheet 2 cme-57m W/LL mgl/1S 0d- 31.1967 4 c Kl. WILLIAMS 3,349,662

ROTATIVELY-SET ANCHOR yASSEMBLY FOR A MINEl BOLT Filed June 25, 1965 5 Sheets-Sheet 3 cHEsER f. WMZ/750g?" .5y r l United States Patent 3,349,662 ROTATIVELY-SET ANCHOR ASSEMBLY FOR A MINE BOLT Chester I. Williams, 347 Greenbriar SE., Grand Rapids, Mich. 49506 Filed June 23, 1965, Ser. No. 466,368 2 Claims. (Cl. 85-74) This invention relates to the construction of a particular type of rock bolt commonly referred to as a mine bolt. These bolts are normally provided with a forged head, and are usually used to secure the overhead rock formation in tunnels and other excavations, Mine bolts are usually of limited length, and are commonly in one piece. Rock bolts used in holes beyond a depth of twelve feet or so are commonly assembled from a plurality of interconnected segments, and usually terminate at the surface in a nut, rather than a forged head. The presence of a nut, rather than the forged head, has permitted the use of rotatively-set anchor devices at the inner extremity of the bolt assembly, with the anchor being set by rotation of the bolt rod prior to tightening of the nut. The subsequent tightening operation takes place without disturbance of the anchor. In the case of mine bolts, however, the presence of the forged head has prohibited this form of anchor unless provision is made for continued rotation of the bolt with respect to the anchor device after the anchor has been set, in order to tighten the bolt. The arrangements for providing this feature have been unsatisfactory.

The present invention has made it possible to use the most etlicient anchor devices that have been developed for any form of rock bolt. This particular form of anchor device includes a cone-shaped expander in threaded engagement with the inner extremity of the rock bolt, with the minor diameter of the cone facing toward the surface of the hole. An expansible shell surrounds the conical expander, and rotation of the bolt with respect to the expander (caused by frictional drag against the hole of the rock formation) will induce radial expansion of the shell if an abutment can be provided which will prevent axial movement of the shell. The present invention provides for the necessary axial restraint of the expansible shell without interfering with a subsequent tightening of the mine bolt after the anchor has been adequately set. In summary, the degree of restraint of the abutment member with respect to the mine bolt (during the setting ofthe anchor) is limited to an intensity which is adequate to set the anchor device, but does not interfere with the subsequent tightening of the rock bolt. The limitation of the restraint must therefore be set at a point substantially below the tensile strength of the rock bolt, but in excess of the degree of axial restraint necessary to oppose axial movement of the shell as the cone expander advances. The amount of force required for this purpose is usually very minor with respect to the total load which the rock bolt is capable of sustaining. In the preferred form of the invention, the abutment member is in threaded engagement with the end portion of the rock bolt, and is constructed of a material which renders it of a predetermined strength such that either (a) the threads will be stripped `on exceeding the desired loading, or (b) the entire abutment member will be fr angible on exceeding the limit load so that it will then move with relatively small resistance along the rock bolt. Other modifications of the invention are also provided which have the characteristic of displaying a predetermined resistance to axial movement, while permitting subsequent tightening of the bolt by forces exceeding the limitations of the abutment member. `Once the anchor has been set, the forces are directly transferred 3,349,662 Patented Oct. 31, 1967 from the expander through the shell to the rock formation.

The function of the abutment member is no longer needed. The several features of the invention will be analyzed in further detail through a discussion of the particular embodiments illustrated in the accompanying drawing. In the drawing:

FIGURE 1 is a sectional elevation showing the preferred form of the invention in a hole in a rock formation, as initially installed.

FIGURE 2 is a section similar to FIGURE l, but showing an intermediate condition during the setting of the anchor device.

FIGURE 3 is a section similar to FIGURES 1 and 2, but showing the behavior of the components after the anchor has been set, and as the rock bolt is tightened.

FIGURE 4 is a sectional elevation of a modified form of the invention incorporating a frangible abutment member and an inclined thread system on the rock bolt and its engaged components. FIGURE 4 represents the initially-installed condition of the assembly.

FIGURE 5 is a section similar to FIGURE 4, but showing an intermediate condition as the anchor device is being set.

FIGURE 6 illustrates the fully set position of the anchor device, and the further tightening of the rock bolt.

FIGURE 7 is a perspective View showing the abutment member incorporated in the assembly shown in FIGURES 4, 5, y6, and 9.

FIGURE 8 is a further modification of the invention showing an abutment member provided with an element for establishing a predetermined resistance to rotation in threaded engagement.

FIGURE 9 is a modified form of the invention shown in FIGURES 4, 5, and 6, in which a thrust-transfer member is included in the assembly. Referring first to FIG- URES 1, 2, and 3, the rock bolt 10 is shown installed in the hole 11 in the rock formation 12. The threaded end portion 13 of the bolt receives the conical expander 14 in threaded engagement, and a portion of the expander is surrounded by the expansible shell 15. Relative rotation of the rock bolt 10 with respect to the expander 14 will induce axial movement of the expander to the right, as a result of the threaded engagement, and this movement will increase the circumscribed diameter around the shell 15. This shell is normally C-shaped in configuration in cross-section to provide a discontinuity for facilitating the expansion.

During the expansion of the shell 15, it must be held against axial displacement. This accomplished `by the presence ofthe plastic abutment member 16, together with the thrust-transfer ring 17. A portion 18 of the abutment member 16 is in threaded engagement with the rock bolt 10, with the remaining portion 19 being generally cylindrical with clearance over the rock bolt. The abutment member 16 is preferably threaded on to the bolt rod up to the end of the threaded end portion 13, as shown in FIG- URES l and 2. The abutment member is preferably constructed of a plastic material, and is able to withstand only a limited amount of axial loading before the threaded engagement at 18 strips out, and the abutment member 16 then moves axially along the rod with relatively little restraint. The intensity of stress at which this takes place is selected by proportioning the axial length of the threaded engagement at 18 so that a sufcient force is produced to provide the necessary axial restraint to the shell 15 to adequately expand it against the wall 11 of the hole. FIGURE 2 illustrates the Ibeginning of the movement of the expander 14 into the shell 15 under these forces, and FIGURE 3 shows the completely installed position of the anchor assembly. After the anchor has reached the position shown in FIGURE 3, further rotation bolt to the left, in view of the fact that the expander 14 (together with the shell 15) may now be considered as fixed with respect to the rock formation 12. As soon as this condition develops, the abutment member 16 is no longer able to sustain a further increase in axial loading, and the threaded portion 1S strips out as the abutment member 16 moves to the right over the rock bolt 10. This corresponds to a tightening of the rock bolt.

Referring to FIGURES 4, 5, and 6, the rock bolt 20 is shown installed in the hole 21 in the rock formation 22. The conical expander 23 is surrounded over a portion of its length by the expansible shell 24, which is axially restrained by the abutment member 25. The thread system on the rock bolt is defined by the outer surface 26 an-d the inner surface 27. Both of these surfaces are helical, and it will be noted that the surface 26 approaches more closely to a plane perpendicular to the axis of the rock bolt 2f). The surface 27 has much more inclination with respect to the perpendicular plane, and this conformation of the thread is significant in connection with this modification of the invention. During the relative rotation between the rock bolt 20 and the conical expander 23, the forces on the expander are provided by the surface 26. The resistance to the axial movement of the shell 24, on the other hand, are provided (against the abutment member by the sloping surface 27. Due to the inclination of the surface 27, a wedging action is produced which tends to increase the resistance to rotation of the abutment member 25 over that of the exander 23. This relationship will tend to cause the abutment member 25 to remain at one axial position so that resistance to the axial movement of the shell 24 can be provided. Roughly the same axial force (although in opposite directions) is effective against both the expander 23 and the abutment member 25. Because of the difference in inclination of the effective forces transferring this thrust, however, the abutment member will have less tendency to move to the right.

FIGURE 4 illustrates the condition of the assembly as it is initially installed in the hole 21, and it is conceivable that a variety of conditions can exist during the setting of the anchor assembly. It is most `probable that the resistance to rotation provided by the frictional interengagement of the threads between the abutment member 25 and the rock bolt 20 will provide sufficient axial restraint for the shell 24 to induce its expansion as shown in FIG- URE S. As the shell encounters the solid `wall of the hole 21, it is conceivable that the end thrust between the expanded shell 24 and the abutment member 25 may at that time cause the abutment member to rotate on the threaded end of the rock bolt 20. It is also possible, however, that a jamming action might develop which will progressively increase the solidity of the position of the abutment member 25 on the threads. To control this development, a peripheral discontinuity is provided as shown at 26 in the abutment member 25 to invite fracture at this point so that the abutment member can then expand peripherally and disengage itself from the threaded end of the rock bolt, thus permitting the rock bolt to move axially with respect to the abutment member without disturbing the set condition of the expander 2.3 and the shell 24. The depth of this discontinuity is established so that the remaining thickness shown at Z7 will provide the necessary strength for the particular material of which the abutment member 25 is to be made) for establishing the intensity of stress at -which this rupture will take place.

Referring to FIGURE 9, an assembly is shown which is essentially similar to that of FIGURES 4, 5, and 6, except for the interposition of the thrust-transfer ring 28 between the abutment member 25 and the shell 24. This arrangement provides a continuous transverse surface against `which the abutment member 25 can bear, since the ring 28 will bridge across the usual peripheral discontinuity in the expansible shell 24. With this arrangement, it is somewhat easier to predetermine the intensity of torque transfer as a result of frictional interengagement at this point.

Referring to FIGURE 8, a modified form of the invention is shown in which the rock bolt 29 is installed in the hole 30 in the rock formation 31. The conical expander 32 and the expansible shell 33 are the same as that illustrated in the other modifications described herein. The primary point of difference in the assembly shown in FIGURE 8 is in the abutment member 34. This member is in the form of a conventional device referred to by the trademark Elastic Stop Nut, and is distinguished by the presence of a ring of non-ferrous deformable material 35 which is rotatively and axially fixed with respect to the nut 34. The primary purpose of the material 35 is to establish a predetermined resistance to rotation which is not effected by the vibration. In this instance, however, this feature is utilized to establish a desired degree of resistance to rotation which Iwill generate Suficient endthrust to permit the expansion of the shell 33 against the wall 30 of the hole. After the shell 33 has solidly engaged the wall of the hole 30, further rotation of the bolt 29 would tend to increase the axial forces acting between the abutment nut 34 and the end of the shell 33, and a point will be reached -when the intensity of the forces at this point will produce sufficient frictional torque transfer to rotate the nut along the threaded end portion 36 of the rock bolt as the bolt is tightened following t-he set of the anchor. In all of the modifications discussed herein, the tightening action is usually not distinguished from the setting of the anchor `device during the installation procedure performed by the workman. He simply rotates the bolt with a power wrench, and the setting of the anchor device is the first event that takes place. Continued operation of the power wrench finally causes the bolt to become tightened to the desired degree determined by the setting of the conventional torque-limiting mechanism on the wrench.

The particular embodiments of the present invention which have been illustrated and discussed herein are for illustrative purposes only and are not to be considered as a limitation upon the scope of the appended claims. In these claims, it is my intent to claim the entire invention disclosed herein, except as I am limited by the prior art.

I claim:

1. In combination with a rock bolt having a threaded inner end portion and an anchor device including a coneshaped expander in threaded engagement with said end portion, and also including an expansible shell surrounding at least a portion of said expander whereby axial movement of said expander toward the outer end of said rock bolt in response to relative rotation between said rock bolt and said expander will induce expansion of said shell, a setting device for said anchor comprising:

an abutment member in threaded engagement ywith said inner end over a minor portion of the length of said abutment member, and normally bearing against a surface axially fixed with respect to the axially outer transverse face of said shell, the major portion of the length of said abutment member lying proximate to said shell and having an internal diameter exceeding that of said bolt, said abutment member having limited axial resistance to movement with respect to said threaded end portion during rotation of said rod with respect to said expander, said limited resistance being substantially less than the tensile strength of said rod.

2. A combination as defined in claim 1, wherein said abutment member is formed of a plastic material having substantially less strength than the material of said rock bolt, whereby the threads of said abutment member may be stripped on exceeding a predetermined loading thereof.

(References on following page) 5 6 References Cited 3,042,068 7/ 1962 Smith 85-33 UNITED STATES PATENTS 3,247,754 4/ 1966 Bleser 85--73 12/1914 Rohmer s574 692 742 8/ (EGN ATENTS 4/1930 Mirzan 85-74 5 ana a;

Australla.

1/ 1954 Thomas et a1. 85-84 CARL W` TOMLIN, Primary Examiner.

1/ 1962 Morin et a1. 151--7 M. PARSONS, IR., Assistant Examiner.. 

1. IN COMBINATION WITH A ROCK BOLT HAVING A THREADED INNER AND PORTION AND AN ANCHOR DEVICE INCLUDING A CONESHAPED EXPANDER IN THREADED ENGAGEMENT WITH SAID END PORTION, AND ALSO INCLUDING AN EXPANSIBLE SHELL SURROUNDING AT LEAST A PORTION OF SAID EXPANDER WHEREBY AXIAL MOVEMENT OF SAID EXPANDER TOWARD THE OUTER END OF SAID ROCK BOLT IN RESPONSE TO RELATIVE ROTATION BETWEEN SAID ROCK BOLT AND SAID EXPANDER WILL INDUCE EXPANSION OF SAID SHELL, A SETTING DEVICE FOR SAID ANCHOR COMPRISING: AN ABUTMENT MEMBER IN THREADED ENGAGEMENT WITH SAID INNER END OVER A MINOR PORTION OF THE LENGTH OF SAID ABUTMENT MEMBER, AND NORMALLY BEARING AGAINST A SURFACE AXIALLY FIXED WITH RESPECT TO THE AXIALLY OUTER TRANSVERSE FACE OF SAID SHELL, THE MAJOR PORTION OF THE LENGTH OF SAID ABUTMENT MEMBER LYING PROXIMATE TO SAID SHELL AND HAVING AN INTERNAL DIAMETER EXCEEDING THAT OF SAID BOLT, SAID ABUTMENT MEMBER HAVING LIMITED AXIAL RESISTANCE TO MOVEMENT WITH RESPECT TO SAID THREADED END PORTION DURING ROTATION OF SAID ROD WITH RESPECT TO SAID EXPANDER, SAID LIMITED RESISTANCE BEING SUBTANTIALLY LESS THAN THE TENSILE STRENGTH OF SAID ROD. 